1. Field of the Invention
The present invention relates to RF shutters and more particularly to such shutters which include a multiplicity of individual intersecting conductive beam members end connected with electrostatic switches for low resistance and high open RF circuit impedance.
2. Description of the Prior Art
There are many situations where it is advantageous to be able to electrically vary the RF transparency of a physical surface. For example, an RF energy source hidden behind a variable transparency "shutter" array may be so hidden by maintaining the shutter array in the OFF position up until the moment when the energy is to be transmitted in, for example, a radar situation. The "shutter" as viewed from outside would appear as a solid metal sheet, thereby reflecting the incoming RF signals.
If the shutter is perfectly reflective for most of the cycle and perfectly transmissive for the few microseconds necessary to transmit and receive a radar signal, then the chances for discovery of the source of this RF energy would be significantly reduced.
Desirable properties of a RF shutter array would include: (1) negligible RF attenuation by the shutter array when it is in the ON state, below a few tenths of a dB; (2) very high RF attenuation in the OFF state of approximately -30 to -40 dB (with its attendant highly reflective surface); and (3) broadband microwave operation in both transmission and attenuation.
Another desirable property of a RF shutter array would be the property of inexpensive fabrication in the microelectronic format.
It is well known in the prior art to fabricate in a batch process microelectronic switches.
The U.S. Pat. No. 3,539,705 issued to H. C. Nathanson et al., on Nov. 10, 1970, entitled, "Microelectronic Conductor Configurations and Method of Making the Same" describes small air gap metal structures batch fabricated as part of a microelectronic component. These spaced metal elements can be optionally closed by compression bonding.
A second patent to H. C. Nathanson et al., issued Aug. 1, 1972, U.S. Pat. No. 3,681,134, also entitled "Microelectronic Conductor Configurations and Methods of Making The Same," is a divisional patent of U.S. Pat. No. 3,539,705. This second patent claims the method of fabrication for the device of the first patent, specifically structures and methods of making such structures involving spaced metal members in integrated circuits, such as for cantilever beams in resonant gate transistors.
A United States patent to Heng et al., issued Mar. 12, 1974, entitled "Microwave Stripline Circuits with Selectively Bondable Micro-Sized Switches for In-Situ Tuning and Impedance Matching," U.S. Pat. No. 3,796,976, describes a microstrip line divided into a multiplicity of short sections, each capacitatively coupled to its neighbor by a cantilever switch. These novel switches were of a predetermined length, (equal to fractions of a desired wavelength) and are connected together to shift the phase of energy propagating along their length thereby tuning and impedance matching the microstrip circuits.
As can be seen in the above referenced patents, it is well known in the prior art to fabricate compression bonded microelectronic conductor switches. However, the use of these switches has been limited to their obvious use as switching devices in electrical circuits.
The problem to be solved therefore is the problem of the protection and hiding of the existence of a radio frequency transmitting means during its operation without interference with the transmitting means effective operation while it is being protected.